Spectrum requires that I use their newest modem.  It only has one ethernet port which plugs into a separate Spectrum router.  That router has four additional ethernet ports, one of which connects to my Deco M4 and I use the other ports for various other wired connections.  I obviously do not need their router for wifi, but I do need the additional ethernet ports as both of my Deco ethernet ports are currently in use (one to connect to the Spectrum router, one to connect a second Deco with a wired connection).  Spectrum modem>Spectrum router>Deco M4

I tried replacing the Spectrum router with a TP-Link ethernet switch.  The port lights on the switch indicate that there is throughout, but there in no internet connectivity on my Deco (solid red light).  Spectrum modem>TP-Link switch>Deco M4

I would like to remove the Spectrum router if possible. I don't need it for wifi and also Spectrum said I could send it back and knock some $ off my monthly bill.  All it really is at this point is a pass through.  But I do need the additional ethernet ports.

Suggestions?